Simply compression means to take a big file and compress it and make it smaller. If you are filming in HD you end up with a big file size this takes up loads of storage and will take a long time to transfer. When you compress it, it can cut the file size significantly. This then will take up less storage and can be transferred faster.
There are two ways to compress a video Spatial compression also know as intraframe and Temporal compression which is also know as interframe. Intraframe is only applied to individual video frames it uses the same process as what is used in a picture. It compresses each still picture and lines them up to use in the video. Intraframe compressions works the same as interframe compression as it gives pixels instructions on what to do. It gives instructions out such as staying the same, rotating and changing colour. There are “I” frames “B” frames and “P” frames. B frames are predictions between the “I” and “P” frames and use a quarter less data as “I” frames. Bitrates are the amount of data being used every second. If a video has a low bitrate it will be low quality. If a video has high bitrates it will be high quality. So the higher the bitrate the better quality video you will get.
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